Overload protective device for an internal combustion engine acting as a drive motor of a main pump of a hydraulic pressure generator

ABSTRACT

An overload protection device for a drive motor of a pressure generator is provided including an auxiliary pump, flow resistance devices, and a pressure-controlled valve. The drive motor drives the main pump of the pressure generator, whose output flow rate is stabilized by a hydraulic regulating valve, which senses the pressure of the output flow of the main pump. The auxiliary pump is also driven by the drive motor and generates an output flow rate proportional to the rotational speed of the drive motor. An auxiliary hydraulic circuit, including the first and second flow resistance devices connected in series, connects the auxiliary pump to the tank of the hydraulic pressure generator. The pressure-controlled valve includes a control chamber connected with a tapping point in the auxiliary hydraulic circuit for sensing the output flow of the auxiliary pump. The pressure-controlled valve is connected with the regulating valve of the hydraulic pressure generator such that if the rotational speed of the drive motor falls below a threshold value, the regulating valve is relieved of a comparison pressure from the main hydraulic circuit connected to the main pump, which will cause the delivery volume of the main pump to be reduced to a minimum delivery level, preventing the drive motor from being stalled.

BACKGROUND OF THE INVENTION

A hydraulically driven thick-material delivery pump, e.g., atwo-cylinder pump for concrete, includes delivery cylinders are eachdriven by a hydraulic drive cylinder, that by whose alternatingpressurization with the outlet pressure from a hydraulic pressuregenerator and depressurization of said drive cylinders to the tank ofthe hydraulic pressure generator a continuous concrete supply isachieved. In the event of a drastic load variation due to malfunctionsoccurring in the area of the thick-material pump, in order to preventstalling of, e.g., a load-sensing main pump of the hydraulic pressuregenerator regulated to a constant flow volume, it is known to detect therotational speed of the diesel engine electronically and when this speeddrops beneath a threshold value considered critical, to control throughan electrohydraulic control device, the delivery volume adjustingelement of the main pump of the hydraulic pressure generator to reducethe volume flow generated by the main pump. This reduces the pump'storque requirement to the point that it can still be supplied by thedrive motor and stalling of the latter can be avoided.

This type of overload protection of the diesel engine and of thehydraulic pressure generator as a whole is, however, overly complex froma technical standpoint and too trouble-prone for the rough operatingconditions under which thick-material pumps must often be operated. Thegoal of the invention therefore is to provide a protective device of thetype recited at the outset which, though simple in design, providesreliable overload protection for the hydraulic pressure generator, andin particular prevents its drive motor from stalling.

The overload protection device for the drive motor in accordance withthe invention includes an auxiliary pump, flow resistance devices, and apressure-controlled valve. The drive motor drives the main pump of thepressure generator, whose output flow rate is stabilized by a hydraulicregulating valve, which senses a pressure drop across a choke in themain hydraulic circuit connected to the main pump. The hydraulicregulating valve adjusts the output flow of the main pump such that whenthe pressure drop across the choke increases, the output flow rate ofthe main pump is reduced and when the pressure drop across the chokedecreases, the output flow rate of the main pump is increased.

The auxiliary pump is also driven by the drive motor and generates anoutput flow rate proportional to the rotational speed of the drivemotor. An auxiliary hydraulic circuit, including the first and secondflow resistance devices connected in series, connects the auxiliary pumpto the tank of the hydraulic pressure generator. The auxiliary hydrauliccircuit includes a tapping point at which flow pressure in the auxiliaryhydraulic circuit may be sensed. The pressure-controlled valve includesa control chamber connected with the tapping point of the auxiliaryhydraulic circuit. The pressure-controlled valve is connected with theregulating valve of the hydraulic pressure generator and to the mainconsumer circuit connected to the main pump of the pressure generator.The pressure-controlled valve is biased by a pretensioned valve springinto a basic position that causes the second control chamber of theregulating valve to be relieved of the comparison pressure in the mainconsumer circuit. By charging the control chamber of thepressure-controlled valve with pressure prevailing at the tapping pointof the auxiliary hydraulic circuit, the pressure-controlled valve may bemoved into a functional position in which the comparison pressureprevailing in the main consumer circuit may be applied to the secondcontrol chamber of the regulating valve. With the overload protectiondevice, if the rotational speed of the drive motor falls below athreshold value, the output flow generated by the auxiliary pump willnot hold the pressure-controlled valve in a functional position. Thepressure-controlled valve will instead move to its basic position,causing the regulating valve to be relieved of the comparison pressurefrom the main hydraulic circuit. The delivery volume of the main pumpwill as a result be reduced to a minimum delivery level, preventing thedrive motor from being stalled.

The overload protection device operates reliably and can be provided ata relatively low cost.

In accordance with one embodiment of the invention, the first flowresistance of the auxiliary hydraulic circuit is connected to a pressureoutlet of the auxiliary pump, and the second flow resistance isadjustable and is connected between the first flow resistance and thetank of the hydraulic pressure generator for sensing the flow rate ofthe auxiliary pump. A simple control valve designed for use at lowcontrol pressure levels will suffice for use as the pressure-controlledvalve.

In accordance with another embodiment of the invention, the second flowresistance of the auxiliary hydraulic circuit is adjustable andconnected to a pressure outlet of the auxiliary pump and the first flowresistance is positioned in the auxiliary hydraulic circuit betweensecond flow resistance and the tank of the hydraulic pressure generator.Although a valve designed for high control pressure levels may berequired for the pressure-controlled valve, it may be integrated in theauxiliary pump, and provide more sensitive control.

In accordance with another embodiment of the invention, thepressure-controlled valve may comprise a differential valve.

In accordance with another embodiment of the invention, thepressure-controlled valve may be designed as a proportional valve.

In accordance with another embodiment of the invention, thepressure-controlled valve comprises a 3/3-way valve, which, between thebasic position, in which the regulating valve is cut off from thecomparison pressure in the main consumer circuit and is connectedinstead with the tank of the hydraulic pressure generator, and thefunctional position, in which the regulating valve is connected with thecomparison pressure in the main consumer circuit but is cut off from thetank of the hydraulic pressure generator, the pressure controlled valvealso has a blocking functional position, in which the regulating valveis cut off from both the comparison pressure of main consumer circuitand the tank of the hydraulic pressure generator. Thepressure-controlled valve may include a valve body with switchingpositions in which the pressure-controlled valve moves from the blockingfunctional position to the basic position or alternately to thefunctional position, such that when looking in the displacementdirection of the valve body, the switching positions are arranged at aninterval from one another equal to between 1/50 and 1/5, preferably1/10, of the total stroke that the valve body can execute between endpositions corresponding to the functional or basic positions. With thisarrangement, oscillations of the outlet flow from the main pump may beavoided at low rotational speeds of the drive motor.

In accordance with another embodiment of the invention, the first flowresistance of the auxiliary hydraulic circuit comprises arotational-speed-synchronous consumer, and the pressure drop across thesecond flow resistance of the auxiliary hydraulic circuit is between 5%and 15%, preferably 10%, of the pressure drop developing across therotational-speed-synchronous consumer during steady-state operation ofmain consumer circuit. This arrangement has been found to increase theenergy efficiency of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an overload protection device for thedrive motor of a main pump of a hydraulic pressure generator inaccordance with one embodiment of the invention.

FIG. 2 is a schematic diagram of an overload protection device for thedrive motor of a main pump of a hydraulic pressure generator inaccordance with another embodiment of the invention.

DETAILED DESCRIPTION

The hydraulic pressure generator shown in FIG. 1 and represented as awhole by 10 for a consumer 11 indicated schematically, for example as atwo-cylinder thick-material pump for conveying concrete, comprises amain pump 12, automatically adjustable with regard to its deliveryvolume per stroke or revolution, said pump being drivable by means of adiesel engine 13.

Main pump 12 is assumed to be a swash plate-axial piston pump, which iscontinuously adjustable to different delivery volumes by pivoting itsswash plate, represented by double arrow 14, said values beingadjustable between a minimum value Q_(min) and a maximum value Q_(max).The position of swash plate 14, indicated by the dashed lines andcorresponding to minimum delivery volume, is the one in which its normalline runs parallel to the axes of the axial piston pump elements, notshown. In the position corresponding to maximum delivery volume Q_(max)of swash plate 14, its normal line runs for example at an angle of 30°to the central axes of the axial piston pump elements.

A choke 18 with adjustable flow resistance is connected as a loadsensing element between high pressure outlet 16 of main pump 12 and highpressure supply connection 17, across which choke, during operation ofhydraulic pressure generator 10 and consumer 11, a pressure drop ΔPappears, representing the difference by which the effective supplypressure P_(V) tappable at central tap 19 between choke 18 and highpressure supply connection 17 of consumer 11, is lower than the outletpressure P_(H) of main pump 12 at its high pressure outlet 16.

In the course of delivery volume regulation of main pump 12, its swashplate 14 is adjustable to various pivot positions, in the specialembodiment shown, two linear cylinders 21 and 22, as actuating drives,are provided by means of which oppositely directed moments are exertableon swash plate 14 from whose equilibrium the respective pivot positionsof swash plate 14 and the delivery volume of main pump 12 linked to saidequilibrium result.

Drive pressure chamber 26, axially movably delimited by a piston 23which through piston rod 24 is linked to swash plate 14, of that linearcylinder 21, by whose pressurization swash plate 14 is pivoted toincrease the delivery volume of main pump 12, is permanently connectedby a control line 27 with high pressure outlet 16 of main pump 12. Boththrough the resultant application of the output pressure of main pump 12to the drive pressure chamber 26 and also through a pretensionedcompression spring 28, linear cylinder 21 constantly delivers a forceresulting in a moment that urges swash plate 14 into a positioncorresponding to its maximum delivery volume.

Drive pressure chamber 29 of second linear cylinder 22, by whosepressurization a moment can be generated that urges swash plate 14 intothe pivot position corresponding to its minimum delivery volume, isconnectable through a control valve 31, controlled by pressure andacting as a manometric balance, alternately to (pressureless) tank 32 ofhydraulic pressure generator 10 or to high pressure outlet 16 of mainpump 12.

Due to the linked connection of piston rod 35 of piston 33 forming theaxially movable limit of driving pressure chamber 29 of the secondlinear cylinder, to the swash plate 14 of main pump 12, pretensionedcompression spring 28 of first linear cylinder 21 also acts as thereturn spring for second linear cylinder 22, urging its piston 33 intothe basic position corresponding to the minimum volume of its drivepressure chamber 29.

Regulating valve 31 is designed as a 3/2-way valve, and is urged by avalve spring 34 into the basic position 0 shown, in which drive pressurechamber 29 of second linear cylinder 22 is connected with pressurelesstank 32 of the hydraulic pressure generator and is cut off from highpressure outlet 16 of main pump 12. By pressurizing a first controlchamber 36 of regulating valve 31 with a high outlet pressure P_(H) frommain pump 12, regulating valve 31 is urgeable into its functionalposition I alternative to basic position 0, in which drive pressurechamber 29 of the second linear cylinder is connected with high pressureoutlet 16 of main pump 12 and is also cut off from pressureless tank 32of hydraulic pressure generator 10.

By pressurizing a second control chamber 37 of regulating valve 31 withpressure P_(V) at center tap 19 between choke 18 and consumer 11, saidpressure being decreased slightly from the high outlet pressure P_(H) ofmain pump 12, regulating valve 31 is urged into its basic position 0.

Regulating valve 31 is designed as a proportional valve, in whichincreasing deflection of its valve piston, represented by switch symbol38, from its initial spring-centered end position as basic position 0,initially decreases the throughput cross section of through flow path 39connecting drive pressure chamber 29 of the second linear cylinder withtank 32 until the path is blocked and a further deflection of valvepiston 38, leading to assumption of functional position I, results in anincreasing, i.e., a cross-section-increasing of the opening of throughflow path 41, by which drive pressure chamber 29 of second linearcylinder 22 is connected with high pressure outlet 16 of main pump 12 infunctional position I.

Hydraulic pressure generator 10, which has been explained in terms ofits design, operates when, and as long as, central tap 19 between choke18 and consumer 11 is connected with second control chamber 37 ofregulating valve 31 as follows:

Before diesel engine 13 is switched on and hence prior to activation ofhydraulic pressure generator 10 and beginning of operation of consumer11, connected between adjustable choke 18 and tank 32 of hydraulicpressure generator 10, the two linear cylinders 21 and 22 are in theirbasic positions as shown, corresponding to the maximum delivery volumeof main pump 12, and piston 38 of regulating valve 31 assumes itsspring-centered end position corresponding to maximum throughput crosssection of through flow path 39, corresponding in turn to the basicposition 0 of regulating valve 31.

When diesel engine 13 is switched on, along with the initial activationof main pump 12 linked therewith, as the flowrate of the oil streamdelivered by main pump 12 through choke 18 and consumer 11 rises,pressure P_(H) at the high pressure outlet of the main pump and also atmiddle tap 19 across choke 11 also rises, with pressure differential ΔP,the pressure drop across choke 18, likewise increasing between highpressure outlet 16 of main pump 12 and center tap 19 and/or highpressure supply connection 17 of consumer 11.

As the outlet pressure P_(H) develops at high pressure outlet 16 of mainpump 12, and as soon as the pressure in first control chamber 36 ofregulating valve 31 is sufficient to displace its piston 38 into itsfunctional position I against the relatively low restoring force ofvalve spring 34, the pressure in drive pressure chamber 29 of secondlinear cylinder 22 provided to adjust swash plate 14 increases. Theeffective cross sectional area F₂ of piston 33 of this second linearcylinder 22 is somewhat larger than the effective cross sectional areaF₁ of first drive cylinder 21, with whose drive pressure chamber 28 theoutput pressure developing at high pressure outlet 16 of main pump 12 ispermanently coupled. The amount ΔF by which the effective crosssectional area F₂ of piston 33 of second linear cylinder 22 is largerthan the effective cross sectional area F₁ of first linear cylinder 21is set so that even at relatively low outlet pressures of main pump 12,for example 6 to 12 bars, the force developed by second linear cylinder22 is sufficient to "overpressurize" first linear cylinder 21 and rotateswash plate 14 into the position corresponding to the minimum deliveryvolume of main pump 12. As a result, in the initial phase of activationof hydraulic pressure generator 10, the torque requirement of main pump12 is reduced, lowering the load on drive motor 13 and allowing it toreach its required rotational speed.

With a steadily increasing flow volume through choke 18 and consumer 11,pressure P_(V), tapped off at center tap 19 between choke 18 andconsumer 17, coupled to second control chamber 37 of regulating valve31, rises, whereupon the regulating valve, with the aid of its valvespring 34, again returns to its basic position 0 in which drive pressurechamber 29 of second linear cylinder 22 communicates with supply chamber32, causing swash plate 14 to pivot, increasing the flow volumedelivered by main pump 12. In the stationary state of the flow volumeregulation, the regulating device comprising regulating valve 31, linearcylinders 21 and 22 acting on swash plate 14 of main pump 12, and choke18 connected between main pump 12 and consumer 11 stabilizes the oilflow through choke 18 and consumer 11 to tank 32 of hydraulic pressuregenerator 10 at a level that can be set indirectly by the adjustablepretensioning of valve spring 34 of regulating valve 31. Thus it isimmaterial over a broad adjustment range of choke 18 what its flowresistance is set to.

In addition to the regulating device provided within the framework ofhydraulic pressure generator 10, which stabilizes the flow volumegenerated by main pump 12 at a desired value, even when the loadrepresented by consumer 11 is subject to considerable fluctuation, aprotective device is provided, designated as a whole by 40 which, whenthe output torque of diesel engine 13 is no longer sufficient to drivemain pump 12 to maintain a predetermined outlet flow volume, reliablyprevents diesel engine 13 from stalling, which could lead to seriousoperating problems.

An emergency situation of this kind can arise as a result of amalfunction of consumer 11, but can also occur under control, forexample when choke 18 is automatically adjusted for increased flowresistance in the end phases of such strokes in order to reverse thepiston movements of consumer 11 gently.

Protective device 40 comprises an auxiliary pump 42, driven like mainpump 12 by diesel engine 13 and generating a flow volume proportional tothe rotational speed of diesel engine 13. Between pressure outlet 43 andsupply container 32 of hydraulic pressure generator 10 is a hydraulicseries circuit consisting of a consumer 44, represented by a fixedchoke, and of an adjustable choke 46 across which outlet pressure P_(A)of auxiliary pump 42 drops, with the pressure drops ΔP_(V) and ΔP_(D)appearing across the components of this series circuit, consumer 44, andadjustable choke 46 being proportional to the flow resistances ofconsumer 44 and adjustable choke 46, and together determining outputpressure P_(A) of auxiliary pump 42. The consumer 44 may comprise arotational-speed-synchronous consumer like a hydraulically driven mixer.

In the embodiment shown in FIG. 1, in which consumer 44 is connecteddirectly to high pressure outlet 43 of auxiliary pump 42 and adjustablechoke 46 is connected between consumer 44 and tank 32, protective device40 comprises a control valve in the form of a 3/2-way valve, designed asa pressure-controlled valve, urged into its basic position 0 by apretensioned valve spring 48, in which position second control chamber37 of pressure-controlled regulating valve 31 of hydraulic pressuregenerator 10 is connected with tank 32 of hydraulic pressure generator10, said control chamber 37 being cut off from center tap 19 betweenchoke 18 and consumer 11, and urgeable into its functional position I bypressurization of control chamber 49 with the pressure prevailingbetween consumer 44 connected to auxiliary pump 42 and adjustable choke46, the level of said pressure corresponding to pressure drop ΔP_(D)across adjustable choke 46, in which position the pressure prevailing atcenter tap 19 between adjusting choke 18, serving as a load sensingelement, and consumer 11 is coupled to second control chamber 37 ofregulating valve 31, said chamber 37 being cut off from tank 32 ofhydraulic pressure generator 10.

The protective device described above operates as follows:

As long as the rotational speed of diesel engine 13 is higher than apresettable threshold value, above which stalling of diesel engine 13can be ruled out with sufficient reliability, the pressure drop acrossadjustable choke 46 of protective device 40 and hence the pressurecoupled with control chamber 49 of control valve 47 is sufficient tohold control valve 47 in its functional position I against the action ofvalve spring 48, in which position the pressure applied to center tap 19of the main pump circuit is coupled to second control chamber 37 ofregulating valve 31 and hydraulic pressure generator 10 operates in thenormal, load-sensing regulating fashion.

If the rotational speed of diesel engine 13 drops below theabove-mentioned threshold value, so that the flow volume generated byauxiliary pump 42 no longer suffices to hold control valve 47 in itsfunctional position I by the pressure prevailing between consumer 44 andadjustable choke 46 of protective device 40, so that the valve is movedto its basic position 0 by the restoring force of valve spring 48,second control chamber 37 of regulating valve 31 discharges its pressureinto tank 32 of hydraulic pressure generator 10, whereupon main pump 12is brought to the functional state corresponding to its minimum deliveryvolume and hence to its minimum torque requirement, at which dieselengine 13 can no longer be stalled.

A drop below the rotational speed threshold value that causes controlvalve 47 to move from its functional position I corresponding to normalregulating operation into its basic position 0 to protect diesel engine13 from stalling can be preset by setting a given flow resistance onadjustable choke 46. In a typical design of protective device 40, thecontrol pressure above which control valve 47 switches to its functionalposition I is between 4 and 10 bars.

Protective device 50 shown in FIG. 2 is functionally equivalent toprotective device 40 shown in FIG. 1, but differs from it in its circuitdesign, namely adjustable choke 46, used to set the rotational speedthreshold below which second control chamber 37 of regulating valve 31is relieved of pressure and is connected directly to high pressureoutlet 43 of auxiliary pump 42, and in that consumer 44 is connectedbetween this adjustable choke 46 and tank 32 of the hydraulic pressuregenerator, and further in that control valve 47', which in its basicposition 0 and its alternate functional position I performs the samefunctions as control valve 47 of protective device 40 as shown in FIG.1, is designed here as a differential valve that switches from its basicposition 0 to its functional position I when pressure differentialΔP_(D) between high pressure outlet 43 of auxiliary pump 42 and centertap 51 between adjustable choke 46 and consumer 44 exceeds a thresholdvalue which can be the same as the control pressure that develops in theembodiment shown in FIG. 1 across adjustable choke 46 connected betweenconsumer 44 and tank 32.

Accordingly, in control valve 47' of protective device 50 as shown inFIG. 2, in addition to first control chamber 49' pressurized with theoutlet pressure provided at high pressure outlet 43 of auxiliary pump42, urging control valve 47' into its functional position I, a secondcontrol chamber 52 is provided, pressurized by the pressure prevailingat center tap 51 between adjustable choke 46 and consumer 44, whereuponcontrol valve 47' is urged into its basic position 0, control chambers49' and 52 being designed so that the forces resulting from theirpressurization and action in opposite directions on the valve pistonscease, so that in this control valve 47' the pressure level isdetermined by pressurization of its second control chamber 52, relativeto which the pressure coupled to first control chamber 49' must behigher so that control valve 47' can be switched against the action ofvalve spring 48 to its functional position I. Control valve 47' is alsodesigned so that this pressure differential amounts to only a few bars,6 bars for example.

In the embodiment of protective device 50 according to FIG. 2, controlchambers 49' and 52 of control valve 47' are exposed, in absolute terms,to much higher pressures than control chamber 49 of control valve 47 ofprotective device 40 according to FIG. 1, imposing stricter requirementson the tightness of control chambers 49 and 52. In protective device 50according to FIG. 2, however, it is quite possible to combine controlvalve 47' and adjustable choke 46 structurally with auxiliary pump 42 inan integral design, since consumer 44 is connected hydraulicallydownstream from this hydraulic functional unit.

Both in protective device 40 as shown in FIG. 1 and in protective device50 shown in FIG. 2, control valve 47 or 47' can be designed as aproportional valve, which, following a transition from one of thepossible functional positions, 0 or I, to the other, exposes increasingopening cross sections of effective bypass and/or through flow paths 53and 54, providing for especially gentle and therefore protectiveaccelerating and decelerating characteristics of main pump 12 whenswitching consumer 11 in the main circuit.

In such a design of control valve 47 or 47', the latter, as is not shownin particular, can be designed as a 3/3-way valve, connected between afunctional position 0 in which second control chamber 37 of regulatingvalve 31 is cut off from comparison pressure tapping point 19 of mainconsumer circuit 11, 18, and therefore is connected with tank 32 ofhydraulic pressure generator 10, and functional position I, in whichsecond control chamber 37 of regulating valve 31 is connected withcomparison pressure tapping point 19 of the main consumer circuit, butis cut off from the tank of hydraulic pressure generator 10, and has ablocking functional position II, in which second control chamber 37 ofregulating valve 31 is cut off both from comparison pressure tappingpoint 19 of main consumer circuit 11, 18 and also from tank 32 ofhydraulic pressure generator 10.

In a special design of such a 3/3-way valve, the switching positions inwhich the control valve moves from its blocking functional position IIinto its through flow position 0 or alternatively through flow positionI, looking in the displacement direction of the valve body, are arrangedat a distance from one another that represents between 1/50 and 1/5,preferably 1/10, of the total stroke that the valve body can executebetween its end positions associated with alternate through flowfunctional positions 0 and I.

What is claimed is:
 1. An overload protection device for a drive motorof a main pump of a hydraulic pressure generator, the main pumpincluding a high pressure outlet for an output flow of a medium, whereina hydraulic regulating device is provided for stabilizing the outputflow rate of the main pump and wherein a main consumer circuit isconnected to the high pressure outlet, said main consumer circuitincluding a choke and a main consumer connected in series and leading toa tank such that a pressure drop occurs in the consumer circuit acrossthe choke indicative of the output flow rate of the main pump, whereinan outlet pressure (P_(H)) of the main pump may be tapped at a firsttapping point in the main consumer circuit at the outlet of the mainpump and a comparison pressure (P_(V)) in the main consumer circuitbetween the choke and the main consumer may be tapped at a secondtapping point between the choke and the main consumer, and wherein theregulating device includes a regulating valve for sensing said pressuredrop by comparing the outlet pressure (P_(H)) and the comparisonpressure (P_(V)), the regulating valve having first and second controlchambers, the first chamber being connected to the first tapping pointand the second chamber being connected to the second tapping point, theregulating valve being capable of adjusting a hydraulic positioningdevice in the main pump to change the output flow rate of the main pumpsuch that when the pressure drop across the choke increases, the outputflow rate of the main pump is reduced and when the pressure drop acrossthe choke decreases, the output flow rate of the main pump is increased,said overload protection device, comprising:an auxiliary pump driven bythe drive motor for generating an output flow having a flow rateproportional to the rotational speed of the drive motor; an auxiliaryhydraulic circuit connecting said auxiliary pump to said tank, saidauxiliary hydraulic circuit including therein a first flow resistancedevice and a second flow resistance device connected in series, and atapping point at which flow pressure in the auxiliary hydraulic circuitmay be sensed; and a pressure-controlled valve including a controlchamber connected with said tapping point of said auxiliary hydrauliccircuit, said pressure-controlled valve being connected with saidregulating valve and said main consumer circuit and being biased by apretensioned valve spring into a basic position which causes the secondcontrol chamber of the regulating valve to be relieved of the comparisonpressure (P_(V)) and wherein by charging the control chamber of thepressure-controlled valve with pressure prevailing at the tapping pointof the auxiliary hydraulic circuit, the pressure-controlled valve may bemoved into a functional position in which comparison pressure (P_(V))prevailing in the main consumer circuit may be applied to the secondcontrol chamber of the regulating valve.
 2. The overload protectiondevice of claim 1, wherein the first flow resistance device in theauxiliary hydraulic circuit comprises a rotational-speed-synchronousconsumer.
 3. The overload protection device of claim 2, wherein therotational-speed-synchronous consumer comprises a hydraulically drivenmixer.
 4. The overload protection device of claim 1, wherein the firstflow resistance of the auxiliary hydraulic circuit is connected to apressure outlet of the auxiliary pump, and wherein said second flowresistance is adjustable and is connected between the first flowresistance and the tank of the hydraulic pressure generator for sensingthe flow rate of the auxiliary pump.
 5. The overload protection deviceof claim 1, wherein the second flow resistance of the auxiliaryhydraulic circuit is adjustable and connected to a pressure outlet ofthe auxiliary pump and wherein the first flow resistance is positionedin the auxiliary hydraulic circuit between second flow resistance andthe tank of the hydraulic pressure generator.
 6. The overload protectiondevice of claim 5, wherein the pressure-controlled valve provided forcoupling the comparison pressure (P_(V)) with the second control chamberof the regulating valve comprises a differential valve and, when thecontrol chamber of the pressure-controlled valve is pressurized with theoutlet pressure of the auxiliary pump, the pressure-controlled valve isurged into a functional position whereby the comparison pressure (P_(V))is applied to the second control chamber of the regulating valve, andwhen a second control chamber of the pressure-controlled valve ispressurized, is urgeable into the basic position wherein the secondcontrol chamber of the regulating valve is relieved of the comparisonpressure (P_(V)).
 7. The overload protection device of claim 1, whereinthe pressure-controlled valve includes flow paths for the alternatefunctional and basic positions, wherein cross sections of said flowpaths expand with increasing deflection of the valve body.
 8. Theoverload protection device of claim 1, wherein the pressure-controlledvalve comprises a 3/3-way valve, which, between the basic position, inwhich the second control chamber of the regulating valve is cut off fromthe second tapping point in the main consumer circuit and is connectedinstead with the tank of the hydraulic pressure generator, and thefunctional position, in which the second control chamber of theregulating valve is connected with the second tapping point of the mainconsumer circuit but is cut off from the tank of the hydraulic pressuregenerator, said pressure-controlled valve has a blocking functionalposition, in which the second control chamber of the regulating valve iscut off from both the second tapping point of the main consumer circuitand the tank of the hydraulic pressure generator.
 9. The overloadprotection device of claim 8, wherein the pressure-controlled valveincludes a valve body with switching positions in which thepressure-controlled valve moves from the blocking functional position tothe basic position, and wherein looking in the displacement direction ofthe valve body, the switching positions are arranged at an interval fromone another equal to between 1/50 and 1/5, of the total stroke that thevalve body can execute between end positions corresponding to thefunctional or basic positions.
 10. The overload protection device ofclaim 8, wherein the pressure-controlled valve includes a valve bodywith switching positions in which the pressure-controlled valve movesfrom the blocking functional position to the functional position, andwherein looking in the displacement direction of the valve body, theswitching positions are arranged at an interval from one another equalto between 1/50 and 1/5 of the total stroke that the valve body canexecute between end positions corresponding to the functional or basicpositions.
 11. The overload protection device of claim 8, wherein thepressure-controlled valve includes a valve body with switching positionsin which the pressure-controlled valve moves from the blockingfunctional position to the basic position, and wherein looking in thedisplacement direction of the valve body, the switching positions arearranged at an interval from one another equal to approximately 1/10 ofthe total stroke that the valve body can execute between end positionscorresponding to the functional or basic positions.
 12. The overloadprotection device of claim 1, wherein the first flow resistance of theauxiliary hydraulic circuit comprises a rotational-speed-synchronousconsumer, wherein the pressure drop across the second flow resistance ofthe auxiliary hydraulic circuit is between 5% and 15 % of the pressuredrop developing across rotational-speed-synchronous consumer duringsteady-state operation of main consumer circuit.
 13. The overloadprotection device of claim 1, wherein the drive motor comprises aninternal combustion engine.
 14. The overload protection device of claim13, wherein the drive motor comprises a diesel engine.
 15. The overloadprotection device of claim 1, wherein the first flow resistance of theauxiliary hydraulic circuit comprises a rotational-speed-synchronousconsumer, wherein the pressure drop across the second flow resistance ofthe auxiliary hydraulic circuit is approximately 10% of the pressuredrop developing across rotational-speed-synchronous consumer duringsteady-state operation of main consumer circuit.